1. Field of the Art
The present invention relates to a color printing apparatus capable of printing in different colors, and more particularly to a bidirectional color printer of impact type for impression of clear images using an inked ribbon or ribbons.
2. Related Art Statement
In the art of color printing with inks of different colors, it is a generally recognized requirement to use inks in order of brightness or lightness of their colors, i.e., to effect printing in light colors prior to printing in dark colors, in order to assure clear color printing.
A serial-impact multi-color printing apparatus is known according to U.S. Pat. No. 4,426,168 to Jozuka et al owned by the assignee of the present application. This printer uses a multi-color ribbon having plural transversely spaced longitudinal color portions or stripes of different colors of different values of brightness, and a print head assembly including plural print wire units which are arranged along the print line. The multi-color ribbon accommodated in a ribbon cassette is skewed relative to the print line so that the individual color stripes are fed in opposed relation with the rows of print wires of the corresponding print wire units. The plural color strips are arranged in order of brightness of their colors so that the brightness is increased in one of opposite printing directions along the print line (viz., from left to right). In this arrangement, the printing may be effected bidirectionally along a print line when images to be printed in different colors are spaced from each other. However, when it is desired to print in intermixed colors with overlapping dots of different colors, the color printing should preferably be made in only one of the opposite printing directions (from left to right) in which the brightness of the color stripes is increased. Namely, the printing in the other direction does not provide satisfactory printing results, because dots of relatively dark colors may be formed prior to dots of relatively light colors. Accordingly, the printing efficiency is sacrificed if it is desired to maintain a high level of print quality, or the print quality is sacrificed if it is desired to achieve a color printing at a high speed. Thus, the printer proposed in the above-identified patent is not satisfactory in terms of total performance of printing speed and quality.
Another type of multi-color printer is known according to Japanese Patent Application No. 51-77483 laid open Jan. 17, 1978 under Publication No. 53-4616, wherein a multi-color ribbon similar to the ribbon indicated above is fed along the print line, and their different color stripes are selected by vertically shifting the exposed portion of the multi-color ribbon between a print head and a recording medium. To attain multi-color printing, the print head should be moved over a print line for each of the plural colors that are used for the line. Thus, the printer of this type requires an increased length of time for printing a line of images in different colors, and suffers considerably low color-printing efficiency.